Color plasma display panels (PDPs) are well known in the art. FIG. 1 illustrates a first prior art embodiment of an AC color PDP wherein narrow electrodes are employed on the front panel. More particularly, the AC PDP of FIG. 1 includes a front plate with horizontal plural sustain electrodes 10 that are coupled to a sustain bus 12. A plurality of scan electrodes 14 are juxtaposed to sustain electrodes 10, and both electrode sets are covered by a dielectric layer (not shown). A back plate supports vertical barrier ribs 16 and plural vertical column conductors 18 (shown in phantom). The individual column conductors are covered with red, green or blue phosphors, as the case may be, to enable a full color display to be achieved. The front and rear plates are sealed together and the space therebetween is filled with a dischargeable gas.
Pixels are defined by the intersections of (i) an electrode pair comprising a sustain electrode 10 and a juxtaposed scan electrode 14 on the front plate and (ii) three back plate column electrodes 18 for red, green and blue, respectively. Subpixels correspond to individual red, green and blue column electrodes that intersect with the front plate electrode pair.
Subpixels are addressed by applying a combination of pulses to both the front sustain electrodes 10 and scan electrodes 14 and one or more selected column electrodes 18. Each addressed subpixel is then discharged continuously (i.e., sustained) by applying pulses only to the front plate electrode pair. A PDP utilizing a similar front plate electrode structure is shown in U.S. Pat. No. 4,728,864 to Dick.
Some PDPs have used wider transparent electrodes that are connected to a high conductivity feed electrode. Such an electrode structure is shown in FIG. 2 and includes transparent electrodes 20, which are connected to sustain electrodes 10 and scan electrodes 14, respectively. In the configurations of both FIG. 1 and FIG. 2, the gap between the electrodes defines the electrical breakdown characteristic for the PDP. The width of the electrodes affects the pixel capacitance and, therefore, the discharge power requirements. The wider transparent electrodes 20 provide a means to input greater power levels to the PDP for increased brightness. However, the manufacturing cost of transparent electrodes 20 is much greater, due to the increased number of required processing steps.
Optically, the narrow electrode topology of FIG. 1 produces a significant amount of light on the outside of the electrodes, virtually eliminating any dark areas between pixel sites. By contrast, sustain electrodes 10 and scan electrodes 14 at the edges of transparent electrodes 20 create a shading of the light between the pixel sites, resulting in dark horizontal lines between pixel rows.
U.S. Pat. No. 4,772,884 to Weber et al. illustrates a further PDP design wherein plasma spreading or "coupling" is employed to couple the plasma at an address cell to one of a plurality of pixels that are adjacent to the addressed cell. In such a PDP structure, loop-configured address electrodes and sustain electrodes are employed to enable selective control of plasma coupling. A description of other color PDP structures and modes of operation can be found in "Development of Technologies for Large-Area Color AC Plasma Displays", Shinoda et al., SID 93 Digest, pages 161-164.
When a PDP is placed in a well lit room, the ambient room contrast ratio is the ratio of the peak white brightness divided by the display's dark level. The intensity of the dark level is a function of the display's background glow plus the ambient light reflecting off the display. For the viewer, a display with a poor ambient room contrast ratio will appear washed out, whereas, in a dark room, the same display will exhibit vibrant colors.
Ambient room contrast has traditionally been enhanced by placing a filter in front of the display. Room light is filtered as it comes into the display and is filtered again after it is reflected off the front panel. The panel's active light is likewise filtered, however it only passes through the filter once. The transmissivity of commonly used filters is 50 to 75%. A 50% filter reduces the reflected room light by a factor of 4, but also reduces the display's brightness in half.
Several factors contribute to the reflectivity of a display. The front filter typically has an anti-reflective coating to minimize its reflectance. The panel's reflectance is a combination of the reflectivity of the front plate surface, the electrode material's reflectivity, and the phosphor's reflectivity. Of these, the phosphor's reflectivity contributes heavily to the reflectance due to its light color.
There is a continuing need to improve the contrast of color PDPs without reducing brightness.
Accordingly, it is an object of this invention to provide a color PDP that exhibits enhanced contrast.
It is another object of this invention to provide an improved color PDP which wherein reflectance from a phosphor layer is reduced.